text:
Does the extension of trailing edge flaps increase or decrease the critical angle of attack?

Which graph is the correct representation of the trailing edge flaps' effect on the critical angle of attack? Does their extension increase (as depicted on the first graph) or decrease (as depicted on the second graph) the critical AoA?

@min Then, what about the effect of the leading edge flaps on the critical AoA? You said the increased camber decreases the critical AoA, but the second graph shows extension of the leading edge flap, which also increases the camber of the wing, increases the critical AoA.

@qqjkztd is right, the virtual chord line obtained with the extension of the devices changes the measured angle of attack

I strongly suggest you read How it flies?. It provides insight about how airflow is modified by flaps.

Both right and both wrong, both over simplifications based on unknown airfoils, and so on. Real aerodynamics is complicated and 3 dimensional.
Flaps usually increase the critical angle of attack a few degrees, but they also increase the effective angle of attack for a given pitch. So the net result is that the pitch of the aircraft will be similar at stall with or without trailing edge flaps, but the true AoA will increase.

Yes. But it's better not to involve pitch here: it can be confusing and is not directly relevant. Just AoA is sufficient. The convention for flapped wing is that AoA is always measured with the same reference as for the 'no flap' configuration. The 'effective AoA' concept is handy for explanation, but the end result is that the critical AoA may change either way. Typically it will reduce for simple flaps.


text:
How does leading edge flap increase camber?

From this post, I've learned that the leading edge flap works by increasing the camber of the airfoil. But how exactly does it work? Since it is a flap, I can guess it works by changing the chord line, just like the trailing edge flap does. But how exactly does the chord line change? Does the leading edge move down to below the original leading edge when the leading edge flap is extended?

Your graph shows an exceptionally poor representation of a typical LE device. This answer contains a realistic view of several different types.

Leading edge flaps and droops do increase the camber because when they move, the leading edge actually droops, and with it the leading edge extremity of the chord line, while the mean camber line remains in place for most of the airfoil length:

Droop
The airfoil is dramatically bent down to the point the bottom side is now concave and the top side has a larger convexity.
Effect on the lift coefficient:

For the same angle of attack α, CL is decreased, but it is now possible to reach larger α and with them larger CL. It also means lower speeds are required to generate the same amount of lift.
LE flaps are usually found at the outboard portion of the wing.

More: Aircraft Design, a conceptual approach, Daniel P. Raymer (around page 278 - view it)

Ideally, the zero-lift angle of attack does not change, regardless of LE device angle. Your text and graph suggest otherwise.

@PeterKämpf: So Raymer (page 278) is inaccurate?

No, but you picked the wrong graph and confused the labels. The top right picture on page 278 is relevant here. Otherways he would be in direct contradiction to his Fig. 12.4 on page 264.

Ah, I see, you use the center right picture. That effect is only possible if you redefine the airfoil chord (as you do in your upper picture) but that is confusing and very unusual. You do not redefine the chord line when TE flaps are extended, so you should not for LE devices, either. After all, the wing is bolted to the fuselage the same way, regardless of LE or TE deflection.

What you show in your first picture isn't a leading-edge flap, but, rather, a leading-edge droop.

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text:
What happened to the Boeing 737.X design?
What happened to the B737.X design that depicted a downward nose much like the B787? It is not apparent in the B737 Max 8.

The answer is on the Wikipedia page for B737.X ... hmmm do I downvote for no research effort? Not sure how that works on this particular SE site.

Boeing was considering designing an all-new airplane to replace the 737 around 2020. Having been in production for over 40 years and through 3 major versions, it seemed like it was finally time to leave the 737 type behind.
However, Airbus decided to upgrade the main competition to the 737 to create the A320neo. The A320neo is more efficient than the 737NG and will be entering service in 2016. Boeing watched orders accumulate for the A320neo and felt that they would lose too much market share in the single aisle market if they waited until 2020 to introduce a new plane to compete with the A320neo.
The high number of orders for the A320neo convinced Boeing to scrap the new plane concept, and focus on just new engines for the 737, in order to get a plane on the market to compete with the A320neo. This allowed the 737MAX to be scheduled to enter service in 2017, less than 2 years after the A320neo. While the MAX does not have as many improvements as a new design would have, it has helped narrow the gap in orders to the A320 series. A new plane still 5 or 6 years away while the A320neo enters service would not have nearly as many orders, meaning the Airbus would be quickly increasing their market share with the A320neo.
A similar situation has happened with the 777, although it is still a much more recent design. The 777X is a more significant redesign than the 737MAX, but the update is needed to compete with the new A350 that is already in service.

"The A320neo [...] will be entering service next year." I think you mean this year, right? (As of today.)

@DavidRicherby Now that you mention it, it probably would be a good thing to not use relative terms like "next year" in answers in general. These are supposed to stay around in the web for several years, after all.

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text:
Do airliners stall first at the wing tip?
One of the disadvantages of the sweepback aircraft is the tendency of a stall to occur at the wingtip first. Various high lift devices are added by design to the wings of the sweepback aircraft like Boeing and Airbus airliners to prevent or delay stalls, yet what happens if the aircraft actually stall? Do they stall at the wingtip first or at the wing root? Do the wings of these aircraft feature washout? If they do, is the washout great enough to prevent a wing-tip-first stall? How much washout do they have in degrees?

They are designed to not stall at the tips first. Such a stall behavior would be highly problematic because it causes a pitch-up moment which exacerbates the stall. See the answers to this question how nasty stalls with swept wings can become.
FAR 25.203 describes the required stall characteristics:

(a) It must be possible to produce and to correct roll and yaw by
unreversed use of the aileron and rudder controls, up to the time the
airplane is stalled. No abnormal nose-up pitching may occur. The
longitudinal control force must be positive up to and throughout the
stall. In addition, it must be possible to promptly prevent stalling
and to recover from a stall by normal use of the controls.

Such a behavior is easiest to achieve when separation does not start at the wing tip. Earlier swept wing designs sometimes had trouble to achieve docile stall characteristics which led to the introduction of stick shakers. Today, changing the airfoil shape over span (aerodynamic washout) and wing twist (geometric washout) are combined to ensure that stall starts at the wing root.
Regarding washout: With high-lift devices employed, the low deflection angle of the ailerons on the outer wing results in a strong effective washout. Here it is important to extend the slats over the outer wing to enable it to function well above the stall angle of attack of the clean airfoil. The picture of an A300-600 below should illustrate the point.

A300-600 in landing configuration (picture source)
But even in clean configuration some washout remains and allows the outer
wing to fly at a lower lift coefficient which ensures a decent stall margin. A photo of an airliner wing on the ground might be misleading: The lift forces in flight will twist the swept-back wing such that washout is increased.


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What's the idea behind leaving control of slats and flaps to pilots in autopilot?
When you watch airliners' flight videos on Youtube, you see pilots still control the slats, flaps and landing gear during the climb and landing phases even after autopilot is engaged. Why doesn't autopilot simply control them when it is capable of it with help of the FMS? Why is
their control still left to pilots, who anyway depend on the FMS (if they have one) to figure out the "right" configurations?

Read the accident report for Asiana flight 214 terminating in SFO.  The go on youtube and watch the video about the Children of the Magenta Line.  Then read the accident report for Emirates flight  EK521.  If that doesn't get the idea across, read the accident report for Air France flight 447.  The human beings in row 0 are not supposed to be passengers; they are supposed to be pilots.

@Mins overdependence on automation. Root cause.  Fly pitch and power.  If you've read the accident report, I think you'll come to the same conclusion I did; a pilot tried to fly the FD when the FD was getting bad signal.  Agree with you that training is a significant causal factor to that tragic crash.

@mins There's that word again!

@mins BTW, I agree with your assertion that the problem is not the pilot or the automation. The problem is the pilot and the automation. Seems more reasonable to have the plane do pretty much everything or pretty much nothing. The problem arises when you have automation doing half the work and the pilots doing the other half

@mins Yeah, but we are getting kind of chatty here, and someone looks to have a good answer working.

The key thing is that not every flight is the same. Sometimes the landing gear is left up for longer for noise abatement, sometimes it goes out earlier if more drag is required. On a non-straight in approach it's sometimes a good idea to extend the gear earlier. If the brakes heat up too much on the taxi before takeoff, the gear may need to be left down for a bit for extra cooling.
Flaps are a bit different as they are typically set for a certain speed, but the principle still applies. For example if turbulence is encountered which effects the airspeed, having the autopilot moving the flaps the second the flap movement speed is triggered is unhelpful.
Basically, these are things that require the active judgement of the pilots considering the individual factors of that specific flight. It's impossible to automate all of this satisfactorily even with pre-planning. Even if you could it would further introduce an overreliance on automation for very little gain.

It makes sense to not automate certain flying tasks, because there are two sides to automation:

On the positive side, it prevents routine mistakes.
On the negative side, it can create an unnoticed deviation during malfunctions.

There are flight accidents where automation actually was part of the cause of the accident, for instance the Turkish Airlines 1951 mentioned in this question. Also, the automated fuel trim system in this incident tried to fix the imbalance from a fuel leak by automatically transferring fuel from the stabiliser trim tank into the leaky wing tank, of which the flight crew was unaware.
If the pilots set the configuration of the aeroplane, they are physically involved in setting its state - their fingers and brains will retain this information much more readily when needed in case of emergency, than when a system does it unseeingly.


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What's the pilot's typical reaction time to co-pilot's callouts?
How long does it take on average before a pilot initiates an action in reaction to a co-pilot's callout? Are there any research data on this subject?
I'm asking this question in relation to the V1 speed, or more specifically to figure out whether it's a reasonable procedure to require pilots to continue takeoff (even) when an engine has failed one or two seconds prior to reaching the V1 speed, taking into account their reaction time.

Pilots (other than me) aren't superhero's, so it would be accurate to say that a typical reaction time is the same for any average human being. Usually the problem isn't reaction time though, it is how long it takes to recognize a problem and make the decision to abort. Sometimes you get to V1 and then recognize a problem when you can't rotate and the pilot attempted to fix it before calling for a rejection.

The best research on this is done with real crews & expensive simulators, and I think their results are exactly the proposition you're looking at, namely that the callout "V1" needs to be said something like a second or two before the actual latest-point-of-first-action to reject the takeoff.
The reason that we can't just say, how long does it take me to respond to the other pilot's callout routinely is, it's a different world between the routine stuff and the abort decision close to V1.  As an example, if I'm flying an approach, I know when the callout 100 feet above minimums is coming.  If I'm not badly tunnel-vision on some isolated part of my scan (very, very rare when you're at that point in an approach... not impossible but quite rare), I can see the altimeter unwinding toward the minimums bug, and so when the other pilot makes the callout, I'm ready to reply "going outside."  And I know that a few moments after that, he's going to call out "minimums" and I have my next callout to make.  No surprises, and if you measured how promptly I respond to his callouts, you'll probably get results showing that I'm pretty prompt.
Compare that with the one takeoff in thousands where things are getting weird close to V1, and I'm actually processing the "is this actually worth stopping for now that we're high speed" decision. I've never had to do that in the actual aircraft, but talking to guys who have, there is some very real time compression -- events happen fast. On a normal takeoff, I'm almost always aware of exactly when the "V1" callout is coming.  But if it is "that dark & stormy night" and I'm trying to sort out the difference between fluxing indication, minor burp, or beginning of an engine failure, that will be the time when the "V1" call WILL catch me by surprise, and how quickly I react to it & remove my hand from the throttles may not correlate to how quickly I've taken it off during the last 999 takeoffs.
On a normal takeoff, my habit is a fairly spring-loaded motion where my hand comes up and away from the throttles immediately at the "V1" call, so that if we get the proverbial big bang, lotsa yaw, and the fire bell right after the callout, I'd be able to catch myself & not go reaching back toward the throttles to initiate an abort-after-V1.  So on those days, you might could get away with pushing the callout closer in time to the latest-first-action-to-stop point.  But not every day is going to be like that, so the Boeing procedures build in the greater level of reaction time.
Because taking the aircraft flying even when you had another second or two that you could have stopped it, is generally (looking at the historical track record of takeoffs rejected & takeoffs continued) less dangerous than stopping the aircraft a couple of seconds after you shouldn't have.
References:

Boeing Article
Boeing Slides - 2002 Presentation This has some good time numbers for you

Thank you so much for your wonderful reply and link to the great study sources on V1!

Note that in certification, there is a one second delay incorporated before V1 at which the engine failure (or other event) occurs which gives the pilot time to react.  This is for a well-trained test pilot who is expecting it, and may not always be duplicated in real life.  See this question for a little more background on the certification: https://aviation.stackexchange.com/questions/3564/how-is-minimum-runway-length-related-to-v1


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Was it ever possible to land big commercial jets from the missed approach point during non-precision approach?
When you shoot a non-precision approach, you are expected to maintain the MDA until the missed approach point, and if you have the runway in sight before you get there, you may proceed to land on the runway, and if not, you must perform a missed approach.
My question is: Was it ever possible to land big commercial jets when the pilots spotted the runway right at the missed approach point during non-precision approach?
With the benefit of Visual Descent Point (VDP) and Constant Descent Final Approach (CDFA), most airline pilots today do not need to worry about this, but I'm still curious: Was it possible?
To add, the reason why I'm asking this question is that if a stabilized landing was not possible in some airplanes (big commercial jets), why was and still is the missed approach designated far too close to the runways for stabilized approach on most non-precision approach charts, instead of it simply being designated at the VDP point, when after all it's a "missed approach point"?

I never understood how it could be possible - except of course if you manoeuvre in a way inconsistent with how most airlines these days feel a jet should be operated close to the ground.

Possible? Yes, depending. Advisable? That's a matter of opinion. I suspect most these days would probably say no unless you did a circling maneuver to another runway. And then many (most?) would say that you have no business circling at less than, say, 800 ft AGL in a 747 or the like.
Restating my first answer: Possible? Yes, for some MAPs, with some aircraft, at some weights, at some airports, to some runways, by some pilots, but not if you HAVE to fly a stabilized approach.

Was it ever possible....

What was physically possible in the past—let's say 25 years ago so it's within the context of my experience—is still physically possible today, so I think what you might be asking is whether it was ever done.
While I don't recall ever having done it myself from the exact MAP, I think it reasonable to accept that it would have been done on occasion by some. Back in the 1990s at the two 747 carriers I flew for, we flew non-stabilized approaches when convenient, especially in freighters. Thus, in-close, down low maneuvering was not the no-no that I get the impression that it is today.
Indeed, the IGS 13 approach at Kai Tak in Hong Kong in bad weather meant you'd be popping out of the clouds a few hundred feet above buildings and then having to make a 47° right turn to line up with the runway. The decision altitude was 600 feet as I remember.

Having the missed approach point so close in to the runway does usually make a steep straight in approach but it does give pilots more chance of seeing the required visual references and then being able to do a circling approach instead of straight in.

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text:
Is it correct to say "the up-elevator position decreases the camber of the elevator"?

Aft movement of the control column deflects
  the trailing edge of the elevator surface up. This is usually
  referred to as the up-elevator position.
  The up-elevator position decreases the camber of the elevator (my emphasis)
  and creates a downward aerodynamic force, which is greater
  than the normal tail-down force that exists in straight-andlevel
  flight. The overall effect causes the tail of the aircraft
  to move down and the nose to pitch up. PHAK 6-5

This is an excerpt from PHAK on the elevator. Do you agree with the statement "the up-elevator position decreases the camber of the elevator"? I've always thought the camber of control surfaces indicates their curvature, which is designed by aircraft designers or controlled by pilots using high-lift devices, and it is the angle of attack that that changes when pilots give control inputs. So isn't it more correct to say "The up-elevator position decreases the angle of attack of the elevator"?

@mins The author of the handbook confused the term "elevator" (= moving part) with "empennage" (= the whole shebang). The correct sentence is of course: The up-elevator position decreases the camber of the empennage.

You're absolutely correct, camber equals curvature. The camber of the horizontail tail is changed by deflecting the elevator, not the camber of the elevator itself. And yes the local angle of attack changes when the elevator deflects, resulting in an aerodynamic moment.

Both of the approaches are correct.
The camber is a basic geometric concept, useful for understanding flow around airfoils. The airfoil can be the wing, and the deflected trailing edge can be the aileron, flap, elevator, or rudder, etc.
The angle of attack description, that the aoa decreases with up elevator, is also correct. In fact, many basic calculations and preliminary aircraft sizing includes empirical correlations of Deflection to AoA ratio.
Deflection of a trailing edge surface, effectively (though not physically) alters the flow such that the AOA of the undeflected airfoil is increased or decreased, somewhat proportionally.
DATCOM and ESDU are some resources that include empirical approaches to these approaches.

However, you're talking about the stabiliser/elevator, which is an INVERTED airfoil. So elevator-up INCREASES the camber of the airfoil, which generates more (inverted) lift, and forces the tail downwards.


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Why does pitot tube freeze at an altitude whose temperature is way below the freezing point?
It's supposed that Air France 447 crashed into the Atlantic because the pilots stalled the airplane when the frozen pitot tubes forced them to handfly it while cruising through the thunderstorm. But how could the pitot tubes freeze in that high altitude where the temperature was way below the freezing point? Isn't it that ice only forms on the aircraft between slightly above 0 and below -20 Celsius degree?
Edit)
Wikipedia: "Below −20 °C (−4 °F), icing is rare because clouds at these temperatures usually consist of ice particles rather than supercooled water droplets. Below −48 °C (−54.4 °F), supercooled water cannot exist, therefore icing is impossible."

Water can freeze at any temperature below the triple point.  Water can also  exist as a liquid at temperatures down to about -50c when conditions are right.

@J.Hougaard I've editted the post. Thank you.

Ah, your edit coincided with my comment.  The key word in all of that is "rare", not impossible and frequent enough to affect many flights a year.

@Simon Yes I got that wrong but still the quote says icing is impossible below 48 Celsius degree

the atmospherical conditions above a thunderstorm are quite different from the "standard atmosphere" the wikipedia article is based on. for exact details on the differences, I would suggest earthscience.SE

So are you asking if the ambient temperature of the probes was above -50c? Since they iced up, the answer must be yes. Remember that without heating, the probes will be significantly warmer than the surrounding static air due to kinetic heating and compression and air above thunderstorms is very different to "normal" air.  In this case, they would have had the pitot heaters on so the capacity of the drains to clear water was less than the  rate of accretion.

First, AF 447 was flying into the top of a tropical storm. The air was much more humid and warmer than that of the standard atmosphere.
Next, in the absence of seed crystals or nuclei, water vapour or liquid droplets stay in the air down to temperatures of -48.3°C at sea level pressure without freezing. From the linked article:

Droplets of supercooled water often exist in stratiform and cumulus
  clouds. An aircraft flying through such a cloud sees an abrupt
  crystallization of these droplets, which can result in the formation
  of ice on the aircraft's wings or blockage of its instruments and
  probes, unless the aircraft is equipped with an appropriate de-icing
  system. Freezing rain is also caused by supercooled droplets.

So it was the impact with the probe which caused the supercooled droplets to freeze.

For us who live in climates with winters below zero, a cool experiment is to leave a half full bottle of water in your car overnight. In the morning, if conditions are right, you can gently pick up the bottle to see it is still liquid. Give it a shake and it freezes instantly.  Same principle, super cooled liquid is introduced to a nucleation point causing freezing.


text:
Why doesn't ATC use a unified frequency for the same control area?
If you have experience of getting flight following or flying instrument in the US, you might have noticed that approach and center controllers alternate between two or three frequencies for the same control area. For example, I get 118.1 from the tower for flight following one day, and the next day I get 126.0 for flight following for exactly the same route of cross country.
Why don't they just use one frequency for the same control area? Wouldn't that make their job much easier?

Might be dependent on atmospheric conditions as certain frequencies will work better in certain conditions.

@SMS von der Tann Never thought about it. Their frequencies are all VHF, and different atmospheric conditions still make a difference in term of the quality if transmissions?

Probably to manage frequency congestion/controller workload.

There may be one controller working several areas one day and separate controllers on busier days, hence more frequencies needed

What happens when there are a lot of aircraft in the area, and several want/need to communicate at the same time?

@SMSvonderTann The difference between 118.1 MHz and 126.0 MHz is sufficiently small that atmospheric conditions should not cause a major difference in reception given identical equipment over identical paths, and VHF is almost exclusively line of sight. You might expect to experience differences with changes of frequency of several tens of percent or more, but not normally with a <7% difference. The major exception to this would be if the chosen frequency happens to be right in the vicinity of an absorption band in the atmosphere, but I'm quite certain there is no such near the VHF air band.

This situation is due to usually 2+ sectors being worked. Each sector will use its own frequency when split. When these sectors get combined, one of 2 things will happen.

The controller will just work with both sectors frequencies keyed up and be listening on both and transmitting on both and have everyone go to the appropriate frequency for the sector they're in or near.

The controller wants everyone on one frequency and has everyone going into those sector's that they are working to be on just one frequency. Frequency congestion and capability (if the transmitters/receivers are different locations for the different frequencies) are also factors.

It is not likely due to meteorological conditions affecting the physics of the radio waves (as others have mentioned the difference between the top and bottom of the aviation band is not very large, and ATC has no easy way of tuning a frequency on the radio).
In the center environment I am not sure why a certain area would be on one frequency one day and another frequency on another day, unless both the main and backup equipment for the usual frequency was inoperative and they were using an entirely separate standby frequency. Some sectors will have these and some might not. Center sectors are very static, and even if two or more sectors are combined controllers will generally have you use the "proper" frequency for your area. This will ensure proper radio reception and make things easier if the sectors need to be decombined.
In the terminal environment, however, which airspace is owned by which controller (departure, initial approach, final approach, etc) can be highly variable depending on runway configuration. At a smaller Class D or class C there might only be one frequency for the entire TRACON, or an east/west or north/south split that doesn't change. But at a Class B TRACON the controller overlying your tiny airport in the morning might be different from the controller overlying it in the evening.

For the pain of stepping on / being stepped on aircraft on the "other frequency" that one can't hear, it's the perpetual gripe in the cockpit "why don't they just put everybody on one frequency" - but when the transmitters are far enough apart geographically & not easily re-tuned, I can see how that's not a great option. Didn't consider that the remote sites can't change frequencies the same way we do... it would save a lot of frustration & "everybody stand by..." calls if they could!

@Ralph all very true. I don't know if this is the case but I can easily imagine the permanent ATC transmitters and especially antennas being precisely tuned to the proper length for a specific frequency, while aircraft antennas have to work over a broader spectrum and won't be a perfect fraction of a wavelength except for certain frequencies.

In the Center, time of day makes a difference, and so does traffic flow. With less traffic flow, sectors will be combined, and the high altitude area around BFF will go from 134.57 to 135.02, because it's combined with the next sector to the east, and 135,02 has better coverage over the combined airspace (there's only one main/standby set for 134.57 at Cheyenne (CYS), with 1 BUEC (Back Up Emergency Communications) at Crawford, NE.).
135.02 has the Crawford (QHX) site, a site at O'Neill (ONL), one at Rapid City (RAP),and backups at Ainsworth (ANW) and Sundance (SUC). On the mid, 135.02 is used for the Rapid City, Casper and Crazy Woman areas, as well, where 133.67 would be used during the day. This gives coverage for high altitude aircraft from Rock Springs (OCS) to CZI to RAP and east, down to ONL, to Denver (DEN) (you probably knew that one), and back to OCS.
It's a matter of convenience for both the controller and the pilot. Combined airspace means fewer frequency changes, fewer frequency changes means fewer things that can go awry.
Disclaimer: Frequency antennae, in spite of their identifiers, are not necessarily at or near their associated airports. Most are near associated VORs.

Isn’t it possible to couple several frequencies in the states? What you describe as a „matter of convenience“ sounds extremely inconvenient to me because you have to change working frequencies all the time. At our unit we just use all the normal frequencies with combined sectors as well which is in fact the most convenient way: less frequency changes, aircraft are on correct frequencies when opening sectors straight away, no necessity to tell adjacent units your new frequency…

You only change the working frequency in regards to what you assign the pilot. You still monitor and broadcast on the others. For instance, with the BFF high sector, when it combines into the TDD (Thedford) high sector, the TDD sector has 134.7 selected, and broadcasts on it. The tricky part (it's part of the job) is to know if an aircraft is on 134.7 in a combined situation, and get them switched to 135.02, so they can hear other aircraft.

When the sectors are decombined (usually during a slow period before the early push comes through) it's a matter of assigning 134.57 to the wstbound aircraft that are in the BFF sector airspace. No need to change the eastbounds, which are flying into the TDD sector.

Yes I know all of what you mentioned (expect your local UK sectors and freqs ofc) however you didn’t answer my question. Can you couple frequencies or will you just use a single one? You were talking about changing the working frequency while still monitoring and broadcasting on the others. So what’s the whole points of that then when you could just keep all the aircraft on the usual frequency of the sector they enter first?

@pcfreak, when you say "coupled frequencies," are you talking about a rebroadcast system where, say, a pilot transmitting on 134.57 will also be heard by pilots listening on 135.02? To my knowledge we do not have that capability in the US.

@randomhead Exactly, that’s what frequency coupling means. We use this instead of changing our working frequency all the time  It doesn’t matter which frequencies you use though, it could also be 134,710 and 126,265 or even a third or fourth one on top!

"Coupling" frequencies isn't really what we do. You simply select multiple frequencies to broadcast on, if the airspace is combined. You're required to monitor the frequency normally assigned for any given sector you have control of, so the position where sectors are combined must be able to broadcast on all of  their frequencies. "Coupling" frequencies (in an ARTCC) as a technical term, refers to pairing a UHF frequency with a VHF frequency at a given radio site, so that both are activated when the site is used. It's so the military can hear us when we clear civilian aircraft.


text:
Do vtails need twin horizontal trim tabs?
Do vtails need twin horizontal trim tabs?
As vtail aircraft don't have a separate horizontal tail, do they need a trim tab on both rudervators?

Not necessarily.  Although the well-known Beechcraft Bonanza has twin tabs,

Sometimes one trim tab, usually the left one, will be offset slightly while the right tab is flush with the control surface. Slightly "tweaking" the left trim tab angle relative to the right's was a common means of adjusting the rig when the airplane was first flown at the factory as part of production.

the Sonex Waiex homebuilt needs only one:

I have the idea of installing one on EACH ruddervator. For pitch, they are moved together, and perhaps for yaw trim they are moved opposite.

...

I considered this on my Waiex project but rejected it. ...I would have to design some sort of 'mixer' to provide proportional tab input.

...

The Dial-A-Trim system that Sonex sells does a good job for "elevator" trim on the Waiex, is pretty fool proof, is ultra reliable, is cheap, and is light in weight.

No, you can get by with a bungee device in the elevator control circuit "upstream" of the mixer to do the job. Basically a spring that applies stick forward for aft pressure for you, and will tend to hold the surfaces at a given position, for the elevator command part, when you hands are  off the stick (you could put the bungee right at the base of the stick if you wanted). More or less the same as a bungee trim for a conventional tail.
If you use tabs for pitch trim only, you will have one on each surface and each tab move the same amount as if you had a horizontal tail with a tab on each surface. If you wanted to use the tabs for both pitch and rudder trim, you'd have to design a mixing mechanism that would do the same sort of thing as the main control mixer, where moving the rudder trim control creates a yaw bias, and the pitch trim control creates a pitch bias in the gearing of the tabs.
One advantage of tabs is you can build an anti-servo function into the tab's operating geometry that allows you to tailor the control feedback beyond the feedback you get with the surfaces alone. If you wanted to use an "all-flying" V tail, you would have to use tabs that provide both a trimming function and an anti-servo function. The Austria glider is a classic example of this. It has all-flying V tail surfaces (no fixed stabilizers) and large anti-servo tabs that provide for both trim and pitch stability and feedback forces.
If it was for an ultralight, I would just use a bungee spring in the elevator control circuit upstream of the mixer. And a regular tail configuration. The V tail has always been a kind of dead end concept.


text:
Why does the Varieze need a metal wing connector?
Why does the Varieze need a metal wing connector?
If the Varieze has Fibreglass wings and a center spar, why is the connector made of cast metal?

In general, you want a really strong connection between the fuselage and wings or Bad Things™ happen. Metal is much better than fiberglass when it comes to attachment points.

For a concentrated load like a spar fitting where the bending load of the spar is transferred to the fuselage structure through bolts, you need a bearing surface (that is, the bore of the bolt hole) that can handle such a concentrated load in a small package.
Epoxy resin doesn't do that well at this, being "plastic" and you generally want a metal interface if you want the connection to be compact, with nearly all the loads being transferred through two bolts. To do the connection using fibreglass plates say, you would need a much larger and bulkier bolt interface to achieve the same compression/tensile strength with an epoxy/glass matrix.
So, for a connection where you want a single connection point with  two bolts that have to bear massive stresses, like Rutan wing roots, it's sometimes preferred to use a metal alloy plate, and distribute the load from the plate to the composite spar with many fasteners. If the structure is carbon fibre, use of aluminum becomes a problem (galvanic differences) and you may replace the aluminum plate with stainless steel or plated steel and live with a bit of extra weight.
Gliders get around this problem by having the wing spars cross each other in the fuselage and pin themselves together and to the fuselage with a single large pin on each side. Instead of large plates, a metal bushing in the fibreglass in the center of the spar overlapping joint, on each side, to provide a bearing surface for the pins/bolts that is harder and tougher than epoxy resin, is sufficient.


text:
How to construct a mechanical adjustment for a horizontal trim tab before the mixer on a vtail?
How to construct a mechanical adjustment for horizontal trim tabs for a vtail for:

Torque tubes/push rods?
Bungees?

The only ways I can think of are:

Torque tubes/Pushrods:

Use a turnbuckle with a handle to adjust the length of the push rod/torque tube in-between the control stick and the mixer

Bungees:

Add an idler pulley wheel that can be adjusted to increase/decrease the tension in the bungee between the control stick and the mixer.

I'm having difficulty reconciling this question and answer with your other one...


text:
What is the size of a clam shell drag rudder compared to a conventional rudder?
What is the size of a clam shell drag rudder compared to a conventional rudder?
This is for a ga aircraft.

Not sure I understand your question, but wouldn't the answer depend on the specific dimensions of the aircraft? The effectiveness of both conventional and clam shell drag rudder depends largely on the arm length. Thus, the distance of the tail from the centre of gravity or the distance of the clam shell rudder from the centre of gravity is very much driving the effectiveness. For a long tail, small span aircraft the answer will be different than for a short tail / wide span aircraft.


text:
Why do some GA aircraft need weights on the control surfaces?
Why do some GA aircraft need weights on the control surfaces?
I've noticed that the Varieze has weights on its canard(elevator), while the elevator on a Zenith CH650 does not.
What determines whether a control surface needs weights?

Does every control surface need to have a counterweight? and Why are "counterweights" used in aircraft production?

Most will be weighted, but sometimes in a way that you won't notice.
A control surface needs to be balanced around its hinge line.  This prevents the control surface from fluttering.  Since most control surfaces would be trailing edge heavy, they have weights ahead of the hinge line to balance them.
Control surfaces can also have aerodynamic balance -- an L-shaped extension ahead of the hinge line.  This helps to alleviate stick forces, but also helps with the mass balance of the surface.


text:
Does an airplane has to take off from beginning of the runway or it can take off from displaced threshold?
I mean, if the airports declared that there is a displaced threshold of runway ; and airplanes use this length for landing but how about for takeoff?

Can the displaced threshold be used for takeoff?
The part of the runway in front of the displaced threshold must not be used for landing (it can be used from the other direction during roll-out), but it may be used for takeoff:

Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction.

(FAA AIM Chapter 2 - Section 3 - Airport Marking Aids and Signs)
This also follows the ICAO definitions in Annex 14, Volume 1, Attachment A, Volume 1, 3. Calculation of declared distances:

The declared distances to be calculated for each runway direction comprise: the take-off run available (TORA), take-off distance available (TODA), accelerate-stop distance available (ASDA), and landing distance available (LDA).

Where a runway has a displaced threshold, then the LDA will be reduced by the distance the threshold is displaced, as shown in Figure A-1 (D). A displaced threshold affects only the LDA for approaches made to that threshold; all declared distances for operations in the reciprocal direction are unaffected.

(Landing Distances on SKYbrary)
Note that the TODA (TakeOff Distance Available) is unchanged in D, but the LDA (Landing Distance Available) is reduced.
Does it have to be used for takeoff?
No, a takeoff can be performed starting from anywhere along the runway. This is typically called an intersection takeoff. Some airports even have taxiway signs displaying the remaining TORA at some taxiways:

(ICAO Standards - Airfield Information Signs)
Such an intersection takeoff requires ATC clearance and of course that the aircraft takeoff performance calculations are done based on this intersection. See also Are intersection takeoffs less common in the USA than in other countries?

Your answers were great but I think that I asked my question wrong; my question actually was: If there is a displaced threshold for a runway; can pilot start their rollout from the beginning of the runway(behind of the displaced threshold) or he/she has to take a clearance beginning of the displaced threshold and start to roll-out? thanks in advance for your answer

@VolkanEroğlu I see, I misunderstood that. I added another paragraph ;)

Is there also a "displaced threshold" for takeoffs?

@zymhan As in an area that can only be used for landing, but not for takeoff? Not that I know of.


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Why is ARP (Airfield Reference Point) needed?
An airport reference point is the centre point of an airport, located at the geometric centre of all the usable runways. The ARP is computed as a weighted average of the end of runway coordinates.

What coordinate would you propose when somebody asks where an airport is located?

@RonBeyer, why don't make an answer out of that comment?

I don't know which country you are referring to.  These are countries that rely on TERPs for instrument procedures.
From the FAA TERPs Order 8260.3D

Definitions

Airport reference point (ARP). The official horizontal geographic location of an airport. It
is the approximate geometric center of all usable runways at an airport.

Page 2-16: The ARP is used to center the MSA on the airport.
Page 3-7:  The ARP is used to determine the distance requirements of remote altimeter settings.
Page 11-5:  The ARP is used to align the FAC with a circling only approach.
Page 14-31: The ARP is used to center the VCOA (Visual Climb over Airfield)

Sometimes you just need a single lat/lon for "where this airport, is."  The ARP depicts where "the point" for this airport, is on this airport.
Why is that an interesting thing to have on an airport diagram?  Dunno, I've never needed it.  But I suppose somebody might.  Maybe if you were aligning your INS, and you wanted to know if just typing in the airport ID (which pulls the airport coordinates from the data base) would get you close to where you're located, you could compare your location on the airfield with where the ARP is, and decide whether it's worth the trouble or not to measure exactly where you are on the chart.  Of course, with GPS available, there's a much easier way to find your exact present position.  So maybe the ARP has less utility now than in the days before GPS.

One possible use is measuring the distance between airports in a standard way, e.g. the 50NM requirement for (some) US cross countries.

@Pondlife That's a use for having the coordinates -- no shortage of those.  The use for having the ARP depicted on the chart is what I'm not coming up with, other than the (somewhat of a stretch) INS example.

Yes, I agree. Maybe I missed something but the question didn't mention charts so I'm not sure if the OP is asking about the depiction, the use, or both.


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Can anybody give an example about Clearance Expiry Time?
Clearance content is included: callsign, flight path, clearance border(destination aerodrome, available report point, controlled airspace border), flight level along the route or for a specific part of the route, etc. and end time of clearance or clearance expiry time. Can you give an example of a clearance expiry time? How does it end, is there any specific time that is notified by air traffic controller to pilot to pass some specific point? How is it said? can you give me a clearance example?

The current version of the AIM says:

Clearance Void Times:
A pilot may receive a clearance, when operating from an airport
  without a control tower, which contains a provision for the clearance
  to be void if not airborne by a specific time.
A pilot who does not depart prior to the clearance void time must
  advise ATC as soon as possible of their intentions. ATC will normally
  advise the pilot of the time allotted to notify ATC that the aircraft
  did not depart prior to the clearance void time. This time cannot
  exceed 30 minutes.
Failure of an aircraft to contact ATC within 30 minutes after the
  clearance void time will result in the aircraft being considered
  overdue and search and rescue procedures initiated.
EXAMPLE− Clearance void if not off by (clearance void time) and, if
  required, if not off by (clearance void time) advise (facility) not
  later than (time) of intentions.

Let's say you're using a GCO or telephone to contact an ARTCC for your clearance out in a low-population area with little infrastructure making it impossible to contact ATC from the ground via standard radio equipment.  After you receive your clearance, you will hang up the call or change frequencies and break contact with ATC.
Due to the break in communication, they will end your IFR clearance by assigning a void time in case you don't get airborne as soon as expected.  If you delay beyond your void time, you would need to call and get a new clearance that you would expect to have issued with a new void time.  The void time is short enough that the implied intention is for the aircraft to receive the clearance while stopped at the runway's hold short line already prepared for takeoff.

This is most commonly seen when starting your flight plan from a pilot controlled airfield. You can not start your IFR flight plan until you are in controlled airspace. At a controlled airfield, you would have to “hold/wait for release”. At an uncontrolled airfield, you would have from the time of activation until the end time of clearance or clearance expiry time to takeoff and have wheels up. You can not leave the ground one second past that time unless you call ATC for a new time. If you do not leave the ground, you must contact ATC ASAP.This is mainly an issue at fields where radio reception between ATC and aircraft at that field is spotty or nonexistent.
You are to then follow your clearance instructions into controlled airspace. Once you are within both radio reception and controlled airspace, you must either contact ATC, land as soon as practicable within Class G, E, or D (with clearance) airspace, or follow the Radio Inoperative procedures outlined in FAR 91.185. Contact ATC immediately upon landing. You can not deviate from this.
Remember, IFR can only be flown in controlled (A,B,C,D or E) airspace. Only there can ATC provide the required separation necessary for IFR flight. Although VFR Flight Following follows similar rules, VFR Flight Plans do not. Do not mistake this for the Expect Further Clearance time that you would get in flight.

Clearance expire times are very common in non-radar environments such as on Oceanic Tracks.
”CLIMB TO REACH FL370 BY 1325Z, REPORT LEVEL”


text:
Can anyone explain what are the apron taxiway and aircraft holding taxiway with an illustration, please?
Note: There are 3 types of taxiway
1) Apron taxiway
2) Aircraft holding taxiway
3) Rapid exit taxiway

I have never heard of "apron taxiway" or "aircraft holding taxiway". Where did you get these terms from?

This question is perfectly clear. Please don't vote to close just because you don't know the answer!

@Bianfable I am a cadet air traffic controller and I got this information from my airport design and management course.

@J.Hougaard and thanks for your support. I am sorry to see my question was closed; it can be beneficial for aviation lovers :)

An apron is what you wear when you bake cookies to keep the flour off your dress.

Apron taxiways are just taxiways, except they are on the apron. They help planes on the apron connect to the main taxiways or the planes on the main taxiways connect to the apron.
I don't know what you meant by holding taxiways, but I assume you meant runway threshold or runway holding point. In that case, here's your illustration:

Notice how the apron taxiways are only on the apron and how they lead to the main taxiways! Also, the blue circled areas are runway holding points.
Legend:
Yellow lines: Apron Taxiways;
Red line: Runway;
Blue circles: Runway holding points;
Orange lines: Main taxiways and high speed taxiway;
Oh, and the high speed taxiway I just mentioned is the slanted taxiway connecting the rwy and taxiway without a holding point. That would answer your Rapid Exit Taxiway question.
Yes your terms are clear, but they are not the exact terms that we use in aviation. I guess that was why that guy said your terms weren't clear. But, I do understand them. It's just you wouldn't use them if you were an actual pilot.

Thanks for the detailed illustration and expression; it was clear. And for your assumption about holding taxiway I know this used for an apron, and refer the plane's taxi from apron to apron taxiway maybe; I do not know clearly; and you understand me correctly, thanks for that. That guy didn't know what I meant; because these are detailed information; and in aviation nobody know all info. I am cadet air traffic controller and I got this information from my airport design and management course.

Cool that you're in air cadets! And you're welcome. I mean that guy, he I guess he was just confused. But I think we should forgive him.


text:
What is the 'Downstream Clearance?'
Downstream clearance  means a clearance issued to an aircraft by an air traffic control unit that is not the current controlling authority of that aircraft; but I don't get it so well. Thanks in advance..

Where is this term used, and in what context?  (I have never heard of it before.)

This term is used to clear aircraft to another air traffic region which does not belong to your responsibility (if you are an air traffic controller and you are responsible for your region; I mean this by saying 'your' ) For example when atc have a flight plan for aircraft and if the pilot wants to be cleared for another flight region which is not cleared for the pilot before by another control region unit; first atc can clear to pilot to another region. Of course atc has to coordinate with another unit about situation..

İt shows up generally when operational aircraft (generally they are military) carry out an operation and when it has to be hidden.

Is this an ATC only term?  What country uses this?  I ask because I flew for the US military for 20 years and have never heard the term.  If you could please clarify where you have heard this used it might help.

İt is used for all countries all over the world; then you know that the Adana İncirli military base. In the years of 2002, 2003 the military pilots just took off from İncirli military base and when they arrived at the border of Iraq Flight İnformation Region, they asked for permission to cruise their route.  And yes it is an ATC only term.

Yeah, I did a couple deployments out of Incirlik actually, but still never heard this term.  If there aren't any Turkish ATC people on this site I doubt you will get a good answer.  BTW, not sure what you mean by asking for permission to cruise the Iraqi FIR, but we certainly didn't ask Iraq!

@MichaelHall Let me straight out of this; I meant that to ask us (TURKEY) not Iraq. And the topic was not related to the nation things, a topic that was related to learning sth from experiences. Please stay with topic Captain.

It has been established that this is an internal ATC term, not used by aircrew.  That much is on topic Lieutenant.

The definition you quote is pretty clear to me. But let me try to explain some of the background to help you understand it.
An ATC clearance always contains a clearance limit, which is the point to which the flight is cleared. Before reaching the clearance limit, the flight must obtain a clearance for the next portion of the flight. If that is not possible, the flight must not pass the clearance limit.
In most circumstances, a flight will receive its ATC clearance on ground before departure, and the clearance limit will be the destination aerodrome. The flight is then allowed to depart and continue all the way to its destination. This can be done because there is reasonable assurance that ATC will be able to coordinate the flight all the way through to the destination as the flight progresses.
In some cases, a clearance for (a portion of) a flight cannot be issued very far in advance. One example is clearance to cross larger portions of ocean (oceanic clearances), which are typically based on procedural separation and require the crew to provide very exact time estimates, which is impossible to do before the flight is airborne. Something similar is likely to be the case for certain military flights where some sort of diplomatic clearance is required to enter a countries airspace. Or maybe a flight has to cross the border between two countries that do not cooperate (a bit hypothetical in this day and age, but it might exist somewhere).
The definition of a downstream clearance is quoted in the answer. It means that, while a flight is flying in airspace A heading toward airspace B, the crew must obtain a clearance from the ATC unit in charge of airspace B before entering. This is because the flight will not be coordinated between ATC A and ATC B like most flights. How exactly this is done probably varies from place to place. The crew might contact ATC B on a secondary radio or CPDLC, or maybe ATC A can forward the request and relay the clearance from ATC B. In any case, the crew is responsible for not passing the valid clearance limit before a clearance to continue has been received.


text:
What's the refueling process like for a light aircraft?
This is for a writing project. I've only been able to find descriptions of refueling large jet aircraft. The plane, a de Hallivand DHC-6 Twin Otter, carries 4 passengers, all minors. None have any significant medical issues. I have no knowledge of flight procedure in any form. How would the timeline look for the whole refueling process? How long would it take? Would the passengers have to leave the plane? If so, where would they be required to go?
Thank you very much, anyone who answers; this stuff is gold to an aerial neophyte like me :)

Probably no more than about a half hour to refuel.  I don't know the Otter, but it's probably gravity fueled through a cap atop each wing.  Per your other question, a risk taking pilot smuggling passengers in an urgent situation probably wouldn't be too concerned with deplaning passengers to meet some safety statute.  I might recommend you find a local Twin Otter operator, buy him or her dinner, and pick their brain on these sort of things.  Maybe ask to crawl around the airplane a little.  The details will lend authenticity to your work.

I know I'm not supposed to thank people with comments, but I really do appreciate your answers. Your expertise is clear, and you're taking into consideration the context of the question and the person asking it. Thank you so much.

You are welcome.  I'm curious about your "project", are you writing a novel?

I am indeed. Though it is, of course, fiction, I believe realism is essential in making a novel enjoyable. It makes the writer more credible, grounds the piece with real, gritty details, and can even educate the reader to some extent. Also, your SkyVector recommendation worked out great; I have a rough path worked out with 7 stops, all of which fall within the 771 NM range except for one, which is 772. I'll make this an important plot point.

The DHC-6 Twin Otter has two fuel tanks located in the belly of the fuselage, one forward (1235 lbs or 185 gal) and one aft (1341 lbs or 201 gal). There is a fuel fill port on the port side of the fuselage above each tank.
Refueling a plane is similar to refueling a car, except (a) planes can hold a lot more fuel than cars, (b) you rarely completely fill the tanks due to weight limitations, and (c) full service is fairly common.
However, with a very light load and a very long trip, you would completely fill the tanks to maximize range. That can mean 30+ minutes at the pump for a plane this size.
For self service, you taxi over to the self-serve pump, stop the engine(s), insert your credit card, attach the ground wire, insert nozzle, pump however much fuel you need, take the receipt, restart the engine(s), and taxi away.
For full service, typically you park on the ramp or at a terminal, call (on the radio) for a fuel truck, the driver does the fueling while you're parked, and you settle the bill before leaving.
Note: in less developed countries, you will likely have to pay cash (USD is accepted everywhere) before they will give you fuel, especially in large quantities. And a smuggler may not want bank records of their transaction anyway.
Normally, passengers will want to get out at fuel stops to stretch their legs, use the restrooms, get snacks, etc. But it wouldn't be unreasonable for passengers to remain aboard if the story has a reason for them to want to stay out of sight.

And also, if you have a typical high-wing light plane (and I'd hardly call the Twin Otter a light plane), you probably need a stepladder to get the nozzle in the filler neck.

@jamesqf If the tanks are in the high wing, yes. They aren't in the Twin Otter.

I think you mean pounds, not gallons.  That many gallons would suit a 737.

@Harper-ReinstateMonica: indeed, https://www.vikingair.com/twin-otter-information/technical-description says 378 US gallon total capacity , plus an option 89 gallon long-range.

@StephenS: Sure, but the Twin Otter isn't a typical light aircraft, so if the OP decides to change the aircraft type, s/he should know that fueling is likely to be different.

@Harper-ReinstateMonica Fixed, thanks!


text:
How might one fly from KRYN to SDRS in a de Hallivand DHC-6 Twin Otter?
First of all, this is not a flight I'm attempting myself; it's for a writing project. I myself have absolutely no knowledge at all of flight. The plane would depart from Ryan Airfield, Arizona (ICAO: KRYN) and land at Resende Airfield (SDRS). As the de Havilland DHC-6 has a range of only 886.7 miles, I assume a great deal of refueling is required. I have no knowledge of flight, so the logistics of a flight this length, (about 5,900 miles), in a light aircraft, are completely alien to me. Importantly, the passengers on the flight (4) do not have passports, but must still be able to enter the country. I’m guessing this means they’d land at a small airport/airfield. Assume the pilot has connections that allow his passengers to bypass any security at the small/private airport. The most important information would be: how long it would take, where/when they’d need to stop on the way, and where could the final destination be.
Your help is greatly, greatly appreciated! :)
Also, assume the situation is urgent and the pilot is a risk taker. He wants to get his passengers there quickly as possible.

Skipping customs is rather the hard part here. Even many small airports do have custom officials and after crossing border, you are required by law to land at airport that does have one. But you don't want to do that, which means choosing untowered strips and generally avoiding contact with authorities altogether. Contacts most likely to help are in drug cartels that can tell you where you can bribe the authorities and how to avoid the ones that may be less corruptible.

… you also have to make sure there will be some jet fuel waiting for you on the small airports you use as DHC-6 is a turbine aircraft, but most traffic in the small fields is piston aircraft that use avgas.

My pilot is a tricky guy. Due to money, connections (often illegal), and extensive beforehand planning, he'll know the who, what, when, etc. of how to get them through with little to no incident. Perhaps a bad contact could present difficulties, or some other mishap could occur on the pilot's behalf. Thanks for the info, it was very helpful!

You can add some hurried departure when some nosey cops find about them anyway, followed by flying low above the trees to avoid appearing on any ATC's radar and then perhaps searching for some drug lord's strip hidden in the middle of the jungle…

Will they need to fly below/around radar like drug smugglers do, which will drastically reduce range and require a circuitous route? Or is the pilot going to fly normally and just rely on his connections to skip customs at the end?

As time is rather important, I'm guessing he'll just rely on his connections and hope for the best. As I said, he's reckless, so that probably fits best anyway. Thanks again for the suggestions, everyone.

I would recommend that you go to https://skyvector.com/ and create a flight plan.  It isn't too difficult, just click on "Flight Plan" in the top left corner and you should be able to figure out the rest.
You obviously have some familiarity with ICAO airport identifiers, simply look for airports along the way that will keep you under a 886.7 NM leg length, and enter them one by one to build your route.  I would use a cruising speed of around 150KIAS based on a quick Google search of Twin Otter performance.  The website will calculate the times for each leg based on this airspeed.
As far as researching suitable airfields that can provide fuel and other services, that will take quite a bit of additional work.  I don't have a handy reference for you, but you could start by searching for World or Latin American Airport Directories.  I wouldn't expect anyone here to do all that work for you and post it as an answer.  If you have any detailed questions as you go don't be afraid to ask.
Regarding your questions about avoiding immigration authorities, that's up to your fertile imagination to come up with fictional scenarios.  There is no aviation specific way to answer this, and most people would be hesitant to recommend methods to circumvent the law.

If the OP wants more "realism", they can't just pick waypoints 886 NM apart. There are 30 minute (day VFR) and 45 minute (night VFR) reserve requirements. I'd assume they are not flying IFR if they are trying to skip customs. They would also need to take into account winds (head wind), so that they don't run out of fuel getting to an airport.

Good points, but you'll note I said "under 886"...  Also, presuming this is for a work of fiction, the situation is urgent, the flight will be through Latin America, and the pilot is a risk taker I didn't feel it was necessary to educate the author on FAA fuel reserve requirements for IFR vs VFR.

Also, the quoted range is for max cruise power and including IFR reserves, and can usually be extended somewhat by flying slower. Plus, if the author needs to make the stops a bit closer or further to get locations that suit the story, they can write in head- or tailwinds, respectively.


text:
F4u race wing design
Can anyone suggest a good airfoil for racing the F4U Corsair? I'm building an RC model but I want it to be fast unlike scale warbird. Any suggestions on wing design and airfoil would be greatly appreciated. I know I can always throw more power to it but I want the fuselage and wing designed to match.
Thanks

It looks like you already asked this question: I need help designing a modern race wing for the f4u Corsair Because that question was closed as too broad, this one probably will be too, unless you can be much more specific somehow.

I'm very new to aerodynamics and I'm just looking for a good airfoil that would be thinner and faster. I would rather have someone suggest a good airfoil rather than me just trying to make up something on my own. It shouldn't matter if I'm building a full size plane or an RC model.

Of course it does matter. Look into Reynolds number and scaling laws. What I wonder is if you want to build a fast model or a F-4U scale model with a different airfoil. Please explain, after having looked into the aforementioned topics. BTW, cool to have an F100 expert on this site!

Consider posting this question to the "Modeling Science" subforum of www.rcgroups.com.  You may get some useful replies there.

As I said earlier I'm just learning about aerodynamics and I have no idea how to figure out what the Reynolds number would be for just such an airplane. I plan to keep the wingspan between 40 and 45 in. I also want to maintain the gullwing design and shape. I built a lot of race cars in my day so I'm trying to build a sleeper LOL. I want it to look scale but I wanted to be extremely fast.

The MH 24 airfoil has been popular for years at international radio-control pylon racing events.  Just ensure that your chord and airspeed give you a Reynolds number exceeding 400,000.
Because airfoils designed for high speed often work poorly at low speed, consider equipping your model with flaps, to make landing easier.
At lower Reynolds numbers, the Eppler E220 has a good reputation.  It's also easier to build (more tolerant of inaccuracies) than airfoils in the mostly-laminar-flow MH series.


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Why was building the Saab Viggen such an achievement of canard design?
In https://aviation.stackexchange.com/a/80365/20394, @GuyInchbald says "Nevertheless, getting the darn thing into production after 60 years of failure was a staggering achievement."
What was so challenging about the Viggen's canards that it took 60 years of failure? After all the very first planes were canards.
And how did Saab solve The Problem on its way to manufacturing the Viggen?

There is not one problem with the canard layout but a whole rag-bag of problems.
Firstly, it is worth noting that the reason the Wrights built their first Flyers as canards was to make them deliberately unstable. They believed that a plane could not be both stable and controllable; a stable plane would just settle on its course and it would be difficult to change course (This was quite a common belief and was not dispelled for some years). Since they were after controlled powered flight, they went for instability. This they achieved by adding a canard elevator with no extra angle of attack. It was widely recognised that such a flying machine required extreme skill and was too dangerous to take to any speed or height.
When Horatio Barber subsequently introduced his ASL Valkyrie in 1910, he gave his canard that extra angle and stabilised it. It was a safe enough plane by the standards of the day, which is to say no attempt at aerobatics and strictly avoid going near the stall. But it proved a one-off product, with the French style of tail proving much easier to adjust on a prototype and get the production version acceptable.
Many of the design issues arising with a practical canard layout are described in the associated Wikipedia article. If the foreplane carries significant lift, it is likely to stall before the main wing and may disrupt the airflow over the latter. Not only is the main elevator now stalled and useless, but the wing is also losing lift. Such a situation may not be recoverable. On the other hand, if the foreplane does not contribute to lift then the main wing needs to be stable in its own right. A stable wing has other problems, which is why tailless aircraft were also rare. Even if the stall is benign and the foreplane simply drops, pitching the nose down and initiating its own recovery, there is the risk of a phugoid cycle developing in which it bobs up and down with ever-increasing energy until something goes horribly wrong.
Later experimental types such as the FW Ente and MiG Utka were relatively docile, having large enough surfaces with low enough loadings to avoid the worst of the problems. However they were somewhat slow and bumbling. While these experiments might have been developed into practical designs, the necessary research appeared pointless when conventional types were already perfectly adequate.
As engines got more powerful and planes flew higher, faster and further, the potential benefits of the canard led to a re-examination. The combination of good manoeuvrability with a tame stall and high efficiency proved elusive. Types with complex high-lift control canards, such as the Curtiss XP-55 Ascender, sought to avoid these issues but it turned out the canard would still stall under some flight conditions, and when it did so it was lethal.
The canard received new interest in the supersonic era, due to its potential for a smaller wing, higher manoeuvrability and a better CG range than a pure tailless swept or delta wing. But, even with a thin delta wing on something like the North American XB-70 Valkyrie, the core stability and control issues remained. (Concorde would not need much manoeuvrability and got over the CG issue by pumping fuel to and fro, so it would abandon the canard).
Torsten Örnberg at Saab realised that these problems could be overcome by close-coupling the canard to a delta or swept wing, using the canard to positively affect airflow over the main wing, and in particular to create and stabilise lifting vortices at low speeds. From his US patent, filed in 1963:

"This invention relates to aircraft of the delta wing canard configuration and refers more particularly to improvements in aircraft of the type having a thin, sharply swept-back main wing and a secondary wing located ahead of the main wing, which improvements overcome certain heretofore existing problems relating to the stability and controllability of such aircraft."

Part of the reason this worked is because the swept and delta wings are relatively easy to make stable in their own right, and a great deal of work in that area had been carried out during and after World War II. The patent also discusses various problems with other canard arrangements, so I am not going to repeat all that in detail.
What I do suggest is that Örnberg's innovation was a remarkable creative insight into a tangle of issues that had defeated every aeroplane designer since Horatio Barber. Usually, such close-coupling of obstructions in front of the wing causes at least as many problems as it cures, and it appears far from obvious that it would work this time round. I'd go so far as to call it a stroke of genius, and its success after half a century of failure a stunning achievement. Its significance also went well beyond its immediate application to the Viggen, the first canard to enter production since 1910. Suddenly the inhibitions of half a century fell away, other designers began to understand how to think about canards and they started appearing on new combat types and being retrofitted to several derivatives of the Dassault Mirage III. The Viggen inspired Burt Rutan to start a similar revolution in civil aviation. Not bad for a relatively small country which seldom sold its warplanes abroad.

Interesting; I've heard canards being sold as safer because they stall first so the nose pitches down and starts the recovery without necessity of pilot intervention, but you mention in most cases the disruption of flow over the main wing meant it did not actually recover at all, so it wasn't really true.

@JanHudec the real problem seems to be when both main wing and canard stall, leaving one at the mercy of fuselage drag effects around the CG (helps with "conventional" design, hurts with canard design).  The (higher AoA) foreplane stalling first is not a problem, as Barber realized in the 1910 improvement, as long as the main wing is unstalled.  The plane (due to the more forward CG placement) will pitch down and recover.

Amazingly, in those early times, a pitch up stall crash (from very low altitudes) was considered "better" than to pitch down and "nose in".  Later they realized only the latter was recoverable, and, from higher altitudes, survivable.  Even the great Kelly Johnson was sold on canard designs until the "double stall" issue was uncovered with the Ascender.

@JanHudec I don't say that most do, just that in general they may. It was more a case of rather too many designs for comfort failing to recover nicely.

Canard designs shouldn't be summarily classified as "failures" without understanding the entire design of the aircraft.
In the age old struggle of maneuverability vs stability they provide a very useful tool in decreasing excessive pitch stability of delta type aircraft.
In the case of the Viggen, they also enhanced high AoA lift for STOL while also fitting into the supersonic shock cone at top speed.
As with the "tiny tail" debates of modern airliner design, there are 2 considerations for lifting surfaces:  balance of forces around CG (easy) and post stall behavior of the aircraft (critical).
A stalled aircraft will sink from its flight path.  Now previously non-lifting forces also act on the CG.  When they are behind the CG, a stabilizing pitch down force is created.  Ahead of the CG ... well, you know!
Adding washout to the rear wing of a canard aircraft will help this quandary (while you're at it, why not put some behind the wing!).
Enter the Canadian goose: Branta Canadensis.  This long distance flyer is classic canard, with its aerodynamic head contributing to lift.  But it's fan shaped tail as at the ready should any directional stability issues arise, other wise it is neatly folded away to reduce drag.

I don't think you mean pitch stability. What the canard allows is a long moment arm for the elevator control forces, making them more effective compared to mounting them on the wing trailing edge. However the Viggen did not use its canard for this purpose.

A canard, movable or not, will reduce pitch stability, which deltas have a lot of.

A slightly off-topic request... do you have any sources of information of the flight characteristics of a Canadian goose? Everything I find in googling is related to the v-formation and I'm more interested in what you describe of the head being a source of lift and the tucking of tail feather in flight to reduce drag. iow, flight characteristics of a single goose, not a flock.

@CGCampbell at 40-50 mph that head will lift (much like the hand out the window).  Folding the tail feathers in (which relaxes stability and reduces drag) is also seen in albatross.  Pitch can then be controlled merely by nodding the head.  The vee formation certainly helps them, and I wonder for a single bird if the head out in front will impart even a tiny bit of extra energy to the wings.  These birds do fly a long way.

@RobertDiGiovanni You are quite wrong on both counts. It is well known that a canard with a higher incidence increases stability, and the pitch stability of sharp deltas is notoriously nonlinear. Can you source those somewhat unusual claims?

@GuyInchbald certainly a shame to dig low on a very constructive question and answer.  1. A "canard of higher incidence" allows CG TO BE MOVED FORWARD.  THAT IS WHAT IMPROVES DIRECTIONAL STABILITY IN ALL AIRCRAFT.  2.  "Pitch stability of deltas is notoriously non-linear": Sir, they have been in use as hang gliders and horizontal stabilizers for over 100 years.  So, one would have to turn attention to your "rag-bag of problems".  Reference:  current Euro fighter designs.


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Can airspeed in ground effect be used to estimate climb performance?
A very interesting crash video (in which everyone survived) shows a Stinson which takes off but is unable to climb out of ground effect.[*]

Watching the video, it seems that the pilot had ample time to put the plane back down in a controlled manner, but was likely stuck in a mindset that "the plane took off and is climbing, we only need a hundred feet more and we're safe". The reality was that the plane was unable to climb out of ground effect, which is why over the 2 1/2 minute flight it never rose above tree height.
Since ground effect enhances lift, it also means that the plane can accelerate and fly faster in ground effect, since less thrust is being used to overcome the induced drag.
Stating the obvious, there is, therefore, some kind of concrete, observable relationship between ground effect performance and climb rate.
The trick is how to quickly recognize in situ that the plane isn't able to climb out of ground effect.

Is there any practical way for the pilot to eyeball estimate the climb rate from the plane's performance in ground effect?
Is there a rule of thumb this pilot could have used to say "I am unable to go accelerate past XXX kts when 5ft from the ground and therefore I know I cannot climb beyond ground effect?"

[*] Google Maps shows that rising terrain was not a factor at the moment of the crash. The airport is at 6370 and the valley is very flat and doesn't rise above 6400' for 5-10 miles in the direction of takeoff.

Proper density altitude and load calculations before takeoff could have saved a Stinson.  Which is to say, this never should have gotten to "I'm off the ground but can't climb."

Absolutely, couldn't agree more.

Not really. You don't really know until you work out the numbers, there being so many variables. Although experience and instinct gets you most of the way there if you have the experience.
He was out of ground effect but was effectively at or above the airplane's absolute ceiling . During his forever takeoff, he used ground effect to gain a bit of surplus energy to allow him to, more or less, zoom climb to about 50 ft, where he found himself with no surplus energy left, on the peak of the power curve, but slipping to the backside of the power curve.  The rest of the flight was slowly consuming the speed margin on the back side of the power curve until he was about to stall and mushed into the trees.  You can see his pitch attitude slowly increasing bit by bit during that whole phase.  He didn't need rising terrain; he put himself into a trap whose only escape was to return to ground effect and eventually land.
The biggest red flag, beyond the sheer length of the ground run, is the part where he lifts off and settles back onto the ground.  If that happens when you are at your normal liftoff speed, the airplane is screaming at you to give up. If he had lots of hours in that Stinson, the instinct that comes from familiarity should have been sufficient to recognize the red flags.
The final red flag is simply the lack of acceleration from thrust above 20 feet or so; instead of zooming to 50 feet on surplus energy, you should feel the plane pulling you faster.
Aside from those clues, the other obvious one is doing the little bit of performance math where he could have determined that he was already at his absolute ceiling in those conditions and needed to wait until a time when the air was cooler. But discarding all that, the skipping takeoff and sluggish acceleration should have been enough warning.
When I was bush flying on floats, in a not-very-rocket-like Cessna 180, there were many times I would be taking off with a very heavy load, on a very hot day, where the performance was marginal even at 1500 ft asl (density alt maybe 4 or 5000 ft, enough to make a float equipped 180 pretty doggy).  I'm on a lake whose length I can only estimate, and I can only estimate my all up weight (coming back from a pickup from a camp).
I would set a reject point, usually about half way down the water run using a shore line landmark.  If the airplane had the performance reserve, you could tell right away as it would come off the water and you could feel it accelerate smartly once clear and would immediately start to climb. Too much of sluggishness there, and I'd fly along in ground effect to see if it improved and put it back down right away (with the shore line looming) if it wasn't accelerating once at about 30 feet or so. Then back to the dock to off load that outboard motor they insisted they bring along.
Sometimes a customer would insist I take all his stuff, and I knew it was way too much, but sometimes you have to find a tactful way to say no, so I would say "let's try it", and go step taxi down the lake with the power reduced (the customer can't tell that you're only at 23" of MP) until the opposite shoreline was looming, say "we won't make it; you don't want us to crash into the opposite shore do you?"  Back to the dock to off-load non-essentials, and no complaints to the boss.

I have watched that video many times but never have I read as concise and useful an explanation as yours here. Kudos sir! Glad I was not aboard. BTW during my time in Winslow, AZ there were two fatal crashes on takeoff in which both planes apparently zoom-climbed out of ground effect and then quickly stalled just off the end of the runway... hot & high. - NN

@nielsnielsen thanks! For the ultimate zoom climb into the back side of the power curve catastrophe, read the NTSB report on the famous CRJ200 incident where they took the empty airplane to its service ceiling by zoom climbing the last several thousand feet to its 41000 ft service ceiling using the autopilot's Vertical Speed mode, instead of letting it take its time by flying in Mach mode, and finding themselves on the back side with no way out https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0701.pdf   Almost the same thing in a way, except at FL410, and with even worse results.

that's awful!  glad I wasn't on board that one either!

I knew the accident investigator that went on site.  The plane hit a meth lab in an out building behind one of the houses, which caused a big fire.  It took GE a while to admit that core lock and poor windmilling ability (due to low ram effect into the compressor inlet) was a problem on the CF-34.  The production flight test procedures had to have a core lock test procedure added to the normal in-flight shutdown/relight tests as a result of this accident.  It also led to an industry wide change in training procedures to add high altitude stall recovery in the sim.

this is ghastly, thanks for sharing this info. i had no idea it was possible to get behind the curve at high altitude. When I was working for HP, I got to fly a couple of times in their rockwell sabreliners (mod 45 and 60 stretch) and once we got an expedited climb profile at low gross weight out of SJO, climbed at like 20 degrees to 41K and then went screaming off to Corvallis. my only cabin mate had a gas problem and I was sitting next to the emergency window exit which leaked like a sieve at 41K so he would let loose with a big one and I would suffer the consequences!

Yes the high flight levels are actually a dangerous place for a pilot not trained.  No thrust margin, little energy margin, aerodynamic damping and stability forces relative to inertial forces are reduced, and TAS is almost double IAS and you have to cover twice as much distance through space, at a given rate of acceleration, to achieve a given increase in IAS.  Your only reserve energy source is gravity.  When you get near stall at FL400, you don't screw around; you dive for speed.

Having read your answer I see no need to add another one. The biggest, reddest flag is the lack of acceleration on the ground already. If that takes too long, don't even take off. Climb speed is less helpful for judging excess power since it depends a lot on flight speed.

I must have misunderstood something my CFI taught me about zoom climbing out of ground effect, because your analysis clearly explains why it’s a bad idea. Thanks!

A bad idea when done at the margins like that at least. Possibly if he'd stayed right on the deck and just let it keep accelerating such as it could, and the plane actually still had a bit of altitude reserve available, and he didn't let it climb until he had a decent energy margin, and the trees weren't there by that time. he'd have been ok.


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what is the disadvantage of blended wing body ,that they not used to achieve more than subsonic speed?
Blended wings have more efficiency than today's wing design,high lift to drag ratio,more efficiency,less fuel rate ,it have lot of advantages so why not they used for commercial airplanes as well as military aircraft rather than UAV.

NO its not i have a different thought?

Now that you have changed the title, you should probably explain what exactly you mean in the detailed text of the question.

What of your question does the accepted answer of the proposed duplicate not answer?

The already question is asked about why not blended wing passenger airplane in operation? i am not suppose to ask  that type,why they not achieve more than subsonic speeds as it have more L/D ratio than today's wing design and what is disadvantages not to acheive supersonic speeds.

@ThangarajSundaramoorthy: But the answer on that question explains that blended-wing-body designs do not have more efficiency that today's wing designs, making the rest of the question pointless.

One of the few production designs that approaches a blended-wing-body was Lockheed Sr-71:

Surprise, with maximum Mach 3.2 it is also the fastest production aircraft ever built.
Because blended-wing-body does not have better L/D at low speed. But generating part of lift with the body has some advantage for high-speed aircraft as it allows smaller wings that is better for high speed (and worse for low-speed).


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Why does a turbine helicopter need to spin a tail rotor?
Should not the exhaust of the turbine supply enough byproduct to deflect and maintain yaw with a simple deflector (i.e. rudder/stabs)?

Well, that’s complex. Where should I begin?

The main job of the tail rotor is to use its long lever arm and directed force/thrust (horizontal lift) to counteract the torque of the spinning main rotor. The exhaust gas of a Turboshaft engine does not produce a large amount of thrust for the very large amount of torque the rotor-powertrain combination produces. See the previous topic: Does a turboshaft's exhaust provide any thrust?.
Energy is finite. In simplest terms, any energy taken out of the engine before the exhaust gasses reach the exhaust nozzle will be energy taken out of the thrust generated. Turbofans generate less thrust with their hot-side core exhaust than Turbojets. Turboprops generate a lot less thrust with their exhaust than Turbofans. And, Turboshafts generate less thrust than that. The most important contribution the exhaust has in a Turboshaft is to dispel heat and waste from combustion.
NOTAR (No Tail Rotor) helicopters already exist that use Coandă Slots and ducted thrust instead of a tail rotor. An internal fan is used instead of the exhaust, though.
The anti-torque thrust a helicopter creates must be variable with the ability to fine tune.
If the engine fails, you still need yaw control until you land.
As complex, damage-prone, maintenance-dependent, and expensive the typical tail rotor system is, if it were possible to use your idea with today’s engine technology, it would have already been done.
I am sure there are other reasons. But, great question. Way to think out of the box.

#3 is very important, the power of the engine and the torque of the main rotor do not increase proportionally.  e.g. if you increase the pitch of the rotor blades, you increase the torque for the same amount of power. So you'd have to have enough torque from the exhaust to counteract the rotor at maximum pitch angle, whilst also being able to do something else with that exhaust at minimum pitch angle. So you're going to need some sort of thrust vectoring system which would be heavy, expensive, and prone to failure.

@JeffUK Increasing the blade pitch increases the torque, the governor keeps the rotational speed constant, torque * RPM = power. The engine power must increase when increasing blade pitch otherwise the rotor speed bleeds out. The tail thrust vectoring unit could be shutter blades at varying angles, pretty simple.

Thrust vectoring via exhaust waste?

The turbine output is very hot and therefore needs to be shielded in some way if it is to be routed through any part of the helicopter.  This shielding adds cost and weight, so it's generally avoided.  The turbine itself is situated very near the center of gravity of the helicopter, so the turbine output has very little leverage on the helicopter's rotation in its current location.
To use the turbine output, it needs more leverage, so it would need to be routed to the end of the tail to a similar location as the tail rotor (which is why the tail rotor is located where it is - to add leverage).  Doing this would mean creating a thermally shielded duct down the inside tail... which would add cost + weight.  You also have the problem that you need to control the thrust from the tail to make the helicopter rotate left and right.  That's not easy if you are using the output from the turbine because that's pretty much fixed unless the helicopter is ascending or descending.
There is a version of helicopter that uses blown air rather than a tail rotor - see the https://en.wikipedia.org/wiki/NOTAR.  This still has the turbine output in the usual place, but uses a fan build into the tail to blow air sideways rather than have an external a tail rotor.  This makes the helicopter much quieter in operation and reduces the risk of injury to persons working around the helicopter whilst it is on the ground with the engine running because there is no tail rotor spinning for them to get injured by.

The turbine engine of a helicopter has very little exhaust thrust. They are turboshafts, designed to extract every bit of useful energy for driving the main rotor shaft. From Wikipedia:

A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power.

A helicopter tail needs to apply between 10 and 20% of the main rotor thrust in order to compensate for the torque of the main rotor. Re-designing the turbine engine to leave enough hot exhaust thrust for the tail is always less efficient than re-directing the extracted main shaft thrust, for instance with a fan driven by a gearbox.

The NOTAR engine uses such a fan, but not to provide all of the required tail thrust - the downwash of the main rotor is deflected sideways, creating a large part of the required anti-torque thrust.

NOTAR is first generation solution that has not been accepted .... compressed air is a new solution and yet utilizing the exhaust of a turbine as a base.... small afterburner perhaps?

Not sure what you mean, there are helicopters using NOTAR. Afterburners are a bit wasteful with fuel.


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Could propellers benefit from the design of the Blue Edge rotor?

Source: wired.com
If indeed the Blue Edge blades reduce noise by 50%, could the similar design be used on [forward-facing] propellers without a penalty in speed or agility?

It would help if you cited your sources here, what blue edge blades are you referring to?

That wiki page linked in the description is the saddest stub I've ever seen. The page on the Airbus H160 gives more info on the rotor design. This does seem to be progressing pretty slowly, given the original announcement for the blade design was a decade ago. There's also a fairly recent paper


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Does waverider have much lower drag than Sears Haack body?
I tried to calculate drag for hyper velocity project using this paper for Sears Haack revolution body. Some parameters:
Diameter: 160mm (round number for simulating 155mm projectile)
Fineness ratio: 13.2, which means projectile's length is 2112mm
From the paper, the assumed wing area $S$ is
$$0.077 \cdot l^2 = 0.077 \cdot (2.112)^2 = 0.3435 \ [m^2]$$
From the Figure 15 in the paper, the total Cd at 2km/s is about 0.004
So total drag at sea level
$$D = 0.5 \cdot v^2 \cdot \rho \cdot S \cdot C_D$$
$$D = 0.5 \cdot 2000^2 \cdot 1.23 \cdot 0.3435 \cdot 0.004 = 3380 \ [N]$$
From the paper, the volume $V$ of the projectile is
$$V = 0.002655 \cdot l^3 = 0.025 \ [m^3]$$
Assume it is filled with aluminum, then the mass $m$ is about
$$ 0.025 \cdot 3000 = 75 \ [kg]$$
So the drag is about 4.5g.
On the other hand, there is an empirical formula for hypersonic lift to drag ratio is:
$$\frac{L}{D} = \frac{4 \cdot (M + 3)}{M} = \frac{4 \cdot (6 + 3)}{6} = 6$$
It seems that if the projectile is shaped as a good waverider then drag can be as low as 1/6 of its weight, assuming the waverider is the best shape for hypersonic lift to drag ratio.
There is of course the problem about scaling where mass is increased at cubed speed, while area only increases at squared speed. While I don't have an complete computational model of waverider to compare directly with SH body, but it seems at the first glance, the waverider can get much lower drag than even the most aerodynamic shape, 1/6g vs 4.5g.
So is it true that the waverider has much lower drag than a SH body?

A waverider will prevent the compressed air under the airframe from escaping sideways. An equivalent view is that the sideways component of the air displaced by the body is used for lift creation by straightening it and pushing it down at the wingtips. This allows it to fly at a lower angle of attack for the same lift, which reduces supersonic lift-related drag linearly with the reduction in angle of attack.
The drag of a Sears-Haack body is the lowest for a given volume and a given fineness ratio. Increasing the fineness (essentially, the local inclination times the circumference of each body section) will reduce drag. This increased fineness, however, will now cause less sideways displacement of airflow which could be used for the waverider effect.
In the end, the question as asked is not answerable. What can be said is:

A blunt Sears-Haack body will profit the most from the waverider effect.
A waverider is still a Sears-Haack body if it has the right cross section distribution over length.
A waverider will maybe lower drag by 20% or 30% in a realistic configuration and at Mach numbers between Mach 3 to 5.

The empirical equation for the L/D of a waverider looks suspicious. Without knowing the constraints of its validity, I would not trust its results. Also, the drag coefficient of your Sears-Haack body looks like the zero-lift drag. You might need to add the lift-related drag to arrive at the complete drag.
And the biggest mistake is to operate it at ground level - 2000 m/s would be appropriate in 30 km altitude. Get the drag figure there and you will arrive at a much lower drag just by operating it in the appropriate density.


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What is the purpose of the ball and string attached to the tip of the vertical fin on test aircraft?
This question applies to aircraft being tested, presumably within a certification program.
I've seen what looks like either a ball or "shuttlecock" at the end of a tether attached to the top/rear extremity of an aircraft's vertical fin. An example can be seen toward the end of this video.
Screenshot from linked video:

What is its purpose? Is it part of or does it contain any instrumentation, or is it there to provide a direct visual indication of something - such as trailing airflow patterns?

That is a static pressure line. The "shuttlecock" device on the end pulls the line out behind the aircraft, where it can get a more accurate pressure reading, away from the air flowing around the aircraft that affects the regular pitot-static system. It will also be more accurate during flight conditions that normal aircraft rarely experience, but need to be accurately analyzed during testing.

Cropped from this image
Static pressure has an effect on the performance of the aircraft, so during testing that is one value they want to measure accurately during flights. Once testing is complete there is no longer a need for that information, and the regular pitot-static system takes the measurements needed.
The line can be seen in this photo, and in this video, you can see the reel inside the rear of the aircraft that is used to pull in the line when it is not in use.

I've seen high-performance aircraft (e.g. jet fighters) fitted with long forward-pointing spikes during testing. I presume they are for the same purpose? If so, what would call for a spike vs a trailing line?

@AnthonyX Yeah, similar purpose, but not identical. The spike is for measuring pitot or impact pressure; the shuttlecock is for static.

Oh OK I thought a spike would have had both pitot and static ports.

@AnthonyX The pitot boom or YAPS boom (the spike) does have both pitot and static ports.  As seen here: https://www.aerosonic.com/products/flight-test-equipment/

Does this cause drag?